MDL-36874 mod_book: Add uarrow() output renderer.

In preparation for Book navigation improvements in MDL-36874, this commit
adds a uarrow() output renderer, to complement rarrow() and larrow().

lib/outputlib.php

@@ -278,6 +278,15 @@ class theme_config {
      */
     public $larrow = null;
 
+    /**
+     * @var string Accessibility: Up arrow-like character is used in
+     * the book heirarchical navigation.
+     * If the theme does not set characters, appropriate defaults
+     * are set automatically. Please DO NOT
+     * use ^ - this is confusing for blind users.
+     */
+    public $uarrow = null;
+
     /**
      * @var bool Some themes may want to disable ajax course editing.
      */
@@ -452,11 +461,13 @@ private function __construct($config) {
             $baseconfig = $config;
         }
 
-        $configurable = array('parents', 'sheets', 'parents_exclude_sheets', 'plugins_exclude_sheets', 'javascripts', 'javascripts_footer',
-                              'parents_exclude_javascripts', 'layouts', 'enable_dock', 'enablecourseajax', 'supportscssoptimisation',
-                              'rendererfactory', 'csspostprocess', 'editor_sheets', 'rarrow', 'larrow', 'hidefromselector', 'doctype',
-                              'yuicssmodules', 'blockrtlmanipulations', 'lessfile', 'extralesscallback', 'lessvariablescallback',
-                              'blockrendermethod');
+        $configurable = array(
+            'parents', 'sheets', 'parents_exclude_sheets', 'plugins_exclude_sheets',
+            'javascripts', 'javascripts_footer', 'parents_exclude_javascripts',
+            'layouts', 'enable_dock', 'enablecourseajax', 'supportscssoptimisation',
+            'rendererfactory', 'csspostprocess', 'editor_sheets', 'rarrow', 'larrow', 'uarrow',
+            'hidefromselector', 'doctype', 'yuicssmodules', 'blockrtlmanipulations',
+            'lessfile', 'extralesscallback', 'lessvariablescallback', 'blockrendermethod');
 
         foreach ($config as $key=>$value) {
             if (in_array($key, $configurable)) {
@@ -533,7 +544,7 @@ public function init_page(moodle_page $page) {
     }
 
     /**
-     * Checks if arrows $THEME->rarrow, $THEME->larrow have been set (theme/-/config.php).
+     * Checks if arrows $THEME->rarrow, $THEME->larrow, $THEME->uarrow have been set (theme/-/config.php).
      * If not it applies sensible defaults.
      *
      * Accessibility: right and left arrow Unicode characters for breadcrumb, calendar,
@@ -546,6 +557,7 @@ private function check_theme_arrows() {
             // Also OK in Win 9x/2K/IE 5.x
             $this->rarrow = '►';
             $this->larrow = '◄';
+            $this->uarrow = '▲';
             if (empty($_SERVER['HTTP_USER_AGENT'])) {
                 $uagent = '';
             } else {
@@ -564,13 +576,15 @@ private function check_theme_arrows() {
                 // So we use the same ones Konqueror uses.
                 $this->rarrow = '→';
                 $this->larrow = '←';
+                $this->uarrow = '↑';
             }
             elseif (isset($_SERVER['HTTP_ACCEPT_CHARSET'])
                 && false === stripos($_SERVER['HTTP_ACCEPT_CHARSET'], 'utf-8')) {
                 // (Win/IE 5 doesn't set ACCEPT_CHARSET, but handles Unicode.)
                 // To be safe, non-Unicode browsers!
                 $this->rarrow = '>';
                 $this->larrow = '<';
+                $this->uarrow = '^';
             }
 
             // RTL support - in RTL languages, swap r and l arrows

lib/outputrenderers.php

@@ -3189,6 +3189,19 @@ public function larrow() {
         return $this->page->theme->larrow;
     }
 
+    /**
+     * Accessibility: Up arrow-like character is used in
+     * the book heirarchical navigation.
+     * If the theme does not set characters, appropriate defaults
+     * are set automatically. Please DO NOT
+     * use ^ - this is confusing for blind users.
+     *
+     * @return string
+     */
+    public function uarrow() {
+        return $this->page->theme->uarrow;
+    }
+
     /**
      * Returns the custom menu if one has been set
      *